As the electric device and the electronic device are being developed to have a small size, a downsized and highly efficient soft magnetic metal powder-compact magnetic core is required. A ferrite core, a laminated electromagnetic steel plate, a soft magnetic metal powder-compact magnetic core (a core prepared by die molding, injection molding, sheet molding and the like) or the like can be used as the magnetic core material for a reactor or an inductor used for applying a high current. Despite a high saturation magnetic flux density, the laminated electromagnetic steel plate has a problem of increased iron loss when the driving frequency of a power circuit exceeds several tens of kilohertz, resulting in a decreased efficiency. In another respect, the ferrite core is a magnetic core material with a little loss at a high frequency, but problems rise such as a big size due to a low saturation magnetic flux density.
The soft magnetic metal powder-compact magnetic core has been widely used because its iron loss at a high frequency is lower than that of the laminated electromagnetic steel plate and its saturation magnetic flux density is higher than that of the ferrite core. In order to downsize the magnetic core, especially the magnetic permeability needs to be excellent at a high magnetic field where direct current is super positioned. That is, the DC superposition characteristic needs to be excellent. In order to get an excellent DC superposition characteristic, it will be effective to use a soft magnetic metal powder-compact magnetic core having a high saturation magnetic flux density. Further, the soft magnetic metal powder-compact magnetic core needs to have a high density. In addition, improving the homogeneity in the interior of the soft magnetic metal powder-compact magnetic core is also effective in the improvement of the DC superposition characteristic.
Thus, it has been disclosed in Patent Document 1 that the homogeneity in the interior of a molded article can be improved if a reactor core formed by particles with an average particle size of 1 μm or more and 70 μm or less, a coefficient of variation Cv (the ratio of the standard deviation of particle size to the average particle size) of 0.40 or less and a roundness of 0.8 or more and 1.0 or less is used. Further, the DC superposition characteristic can be improved.
In addition, in Patent Document 2, it has been described that boron nitride covers the surface of the soft magnetic metal powder to form a coating that can be deformed to a great extent so as to provide a high density. As a result, effects have been produced such as the improvement of magnetic properties.